Path tracking in ultrasound system for device tracking

ABSTRACT

A method for determining a projected track of an object ( 230 ) includes measuring movement from frame to frame of a detected object point in a field of view by periodic comparison of positions, extrapolating a locus of periodically detected object points, and qualifying the locus by calculating and applying a threshold to the linearity in a sequence of positions and a threshold to consistency in strength. The method further produces the plurality of ultrasound images by including thereon a rendering of a plurality of lines ( 310 ) as a path track indicator ( 330 ) on one or more ultrasound images ( 305 ) and displaying the projected track of the object when a user moves the tracked object a minimum distance in a region of interest ( 242 ) of a subject ( 240 ). The method also includes utilizing a motion sensor ( 234 ) with a probe ( 205 ) to suppress calculation and display of the projected track.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a Continuation of application Ser. No. 16/485,463,filed Aug. 13, 2019, which is the U.S. National Phase application under35 U.S.C. § 371 of International Application No. PCT/EP2018/052730,filed on Feb. 5, 2018, which claims the benefit of U.S. ProvisionalPatent Application Ser. No. 62/458,789, filed Feb. 14, 2017. Theseapplications are hereby incorporated by reference herein.

BACKGROUND Technical Field

This disclosure relates to ultrasound devices and more particularly topath tracking in ultrasound systems which have the capability oftracking a device and displaying the position of the device in theultrasound images.

Description of the Related Art

Precise visualization of objects such as needles or catheters andreal-time localization with respect to imaged anatomy are needed forminimally invasive interventions. Intra-operative ultrasound is oftenused for these purposes. Various ultrasound systems are available in themarket which utilize some method for tracking the location of an objectin the body of the patient. Such systems share the common attribute thateach detected position of the object is digitally represented in thesystem, allowing display of the positions, and that the positions areupdated periodically, typically in conjunction with active scanning, sothat the real time ultrasound image display can also show the detectedlocation of the object being tracked. Some systems offer a means ofshowing the path of the detected object in the image, either as history(where the object came from), or future extrapolation (where it will goif moved in the same direction), or both. Generating such a projectedpath is typically by means of a method well understood in the art. Onemethod is to include a mechanical fixture like a needle guide mounted onthe ultrasound probe which simply constrains the object to follow apredetermined path, i.e., to physically constrain the path of the objectwith respect to the ultrasound probe as the object is inserted. Othermeans include locating the device such as by magnetic orelectro-magnetic (EM) sensing of the location of the object with respectto similar sensing of the ultrasound probe position.

These systems suffer from complex, expensive parts and circuitry,susceptibility to interference, positional ambiguity due to thedeformation of the object (such as bending of the needle), workflowburden such as the obligation to calibrate the positional sensing, etc.There is one system which requires no physical registration of therelative positions of the ultrasound probe (and thus the displayedimage) and the object whose position is displayed in the image. U.S.Pat. No. 9,282,946, commonly owned, and incorporated herein in itsentirety, describes a system wherein an acoustic signal from the probeis used to activate an acoustic sensor on the tracked object, and viathe timing of a returned electrical signal from the object, detect theposition of the object with respect to the image itself, therebyobviating all mechanical, magnetic, electromagnetic (EM), or othermechanisms for tracking, and thus also eliminating their cost,complexity, calibration, and susceptibility to error.

In any ultrasound imaging system that also tracks and displays theposition of an object, it would be desirable to show the path of thetracked object throughout the ongoing series of displayed images (i.e.through time) without relying upon positioning fixtures or circuitry todetect the relative position of the object with respect to theultrasound probe. In a system which indeed possesses no such relativeregistration apparatus, such as the simplified, lower cost system ofU.S. Pat. No. 9,282,946, which uses only an acoustic sensor on theobject for position detection, showing the path of the detected objectpresents an unsolved problem. A particular impediment is that while theposition of the object is continuously and accurately located in thedisplayed ultrasound image, the ultrasound probe itself may be rotatedor translated with respect to the object, which is largelyindistinguishable from motion of the object itself in the medium beingscanned.

As further background, a very brief review of ultrasound probes andimaging follows. The versatility of a diagnostic ultrasound system islargely determined by the types of probes which can be used with thesystem. Linear array transducer probes are generally preferred forabdominal and small parts imaging and phased array transducer probes arepreferred for cardiac imaging. Probes may have 1D or 2D arraytransducers for two dimensional or three dimensional imaging. Indwellingprobes are in common use, as are specialty probes such as surgicalprobes. Each type of probe can operate at a unique frequency range andhave a unique aperture and array element count. Some ultrasound systemsare designed for grayscale operation or operation at the transmitfrequency such as for greyscale and color Doppler imaging while otherscan additionally perform harmonic imaging. For each of the intendedimaging modes, the functional characteristics of the probes, such asphysical aperture, transducer element spacing, passband frequencies,etc. determine the requirements for transmitting ultrasound pulses andprocessing the received echoes. The variation in probe characteristicsand functionality means that the processing system operable with avariety of probes must be reprogrammed each time a different probe isput to use.

An example of an object that is tracked during an ultrasound procedureis a needle. During needle biopsy and some interventional therapy,clinicians insert a needle into a subject, such as the body, to reach atarget mass. For regional anesthesia, a needle is used to deliveranesthetic to the vicinity of a target nerve bundle in the body,typically in preparation for a surgical procedure. Usually ultrasoundimaging is used for live monitoring of the needle insertion procedure.To perform a safe and successful insertion, it is necessary to locatethe needle accurately in the guided ultrasound image. Unfortunately, inclinical practice the visibility of the needle itself in theconventional ultrasound image is poor, resulting in difficulty forclinicians to insert the needle accurately. Hence the desirability of aneedle tracking system and further, a means of projecting the path ofthe needle on the image display.

Different techniques have been used to achieve better needlevisualization in ultrasound images, for example, adaptively steering theultrasound beam towards the needle to improve the acoustic reflection ofthe needle and compounding with the non-steered ultrasound image;manipulating the needle surface coating, geometry and diameter toenhance acoustic reflection; providing an extra optical, magnetic, orelectro-magnetic position sensor on the needle to track the needlelocation in the ultrasound image, etc. In these techniques, either aspecially designed needle is used, or an extra position sensor isattached to the needle, or the ultrasound imaging system is manipulatedto enhance the visualization of the needle. Those approaches lead to anincrease of the cost of providing enhanced needle visualization. Incontrast, the simple system mentioned above, which utilizes only anacoustic sensor on the object to provide an electrical signal to thesystem for location detection, reduces the cost and complexity of thetracking apparatus while increasing its accuracy. But it presents thechallenge of how to effectively project the path of the tracked object.

SUMMARY

In accordance with the present principles, an ultrasound probecommunicates with an image processor for producing a plurality ofultrasound images by standard methods known in the art, and alsoprovides a method of detecting an object in the ultrasound image field,preferably without the complexity and cost of an apparatus to measurethe relative position of probe and object, such as by instead utilizingan acoustic sensor in the object. The system then additionally measuresmovement from frame to frame of a detected object point in a field ofview by periodic comparison of positions, extrapolating a locus ofperiodically detected object points, and qualifying the locus bycalculating and applying a threshold to the linearity in a sequence ofpositions and a threshold to consistency in strength. The imageprocessor further produces the plurality of ultrasound images byincluding thereon a rendering of a plurality of lines as a path trackindicator on one or more ultrasound images of the plurality ofultrasound images, displaying the projected track of the object when auser moves the tracked object a minimum distance in a region of interestof a subject, and utilizing a motion sensor in the ultrasound probe ormotion detection from image data to suppress calculation and display ofthe projected track when the ultrasound probe is rotating or translatingin space.

A system includes an ultrasound probe and an image processor forproducing a plurality of ultrasound images by including a pair ofreference lines passing as parallel tangents on opposite sides of alocation circle displayed by the system to locate an object, displayinga projected track of the object as the tracked object moves within aregion of interest of a subject, and utilizing a motion sensor tosuppress calculation and display of the projected track when theultrasound probe is rotating or translating in space.

A method for determining a projected track of an object includesmeasuring movement from frame to frame of a detected object point in afield of view by periodic comparison of positions, extrapolating a locusof periodically detected object points, and qualifying the locus bycalculating and applying a threshold to the linearity in a sequence ofpositions and a threshold to consistency in strength. The method furtherincludes rendering a plurality of lines as a path track indicator on anultrasound image and displaying the projected track of the object when auser moves the tracked object a minimum distance in a region of interestof a subject. The method also includes utilizing a motion sensor in anultrasound probe or motion detection from image data to suppresscalculation and display of the projected track when the ultrasound probeis rotating or translating in space.

These and other objects, features and advantages of the presentdisclosure will become apparent from the following detailed descriptionof illustrative embodiments thereof, which is to be read in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

This disclosure will present in detail the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a block/flow diagram showing an ultrasonic diagnostic imagingsystem, in accordance with one embodiment;

FIG. 2 is a diagram showing a needle tip tracking (NTT) system incommunication with an ultrasound system, in accordance with oneembodiment;

FIG. 3 is a diagram showing an ultrasound image depicting a pair ofreference lines passing as parallel tangents on opposite sides of alocation circle displayed by the system in response to the position ofthe object/needle, in accordance with one embodiment;

FIG. 4 is a diagram showing a needle inserted into a patient with theultrasound probe scanning it “in-plane” or “transverse,” in accordancewith one embodiment; and

FIG. 5 is a flow diagram showing a method for determining and displayinga projected track of an object/needle within a region of interest of anobject, in accordance with illustrative embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

In accordance with the present principles, systems, devices and methodsare provided to track and display a projected track of an object. Thepresent principles provide embodiments where the systems, devices andmethods are self-referential in that they do not rely on an externalpositioning system to determine the validity of the detected path.

In one useful embodiment, an ultrasound system includes an objectlocation apparatus where the object location apparatus utilizes theultrasound acoustic pulses generated by the ultrasound system toenergize the tracking sensor and a method of automatically determiningand displaying the projected track of the object in the scanned medium.The method comprises a) measuring movement from frame to frame of thedetected object point in the field of view by periodic comparison ofpositions, b) extrapolating the locus of periodically detected points,c) qualifying the locus by calculating and applying a threshold to thelinearity in the sequence of positions and a threshold to consistency instrength, d) rendering a plurality of lines or another path trackindicator on the ultrasound image as an overlay, e) using data from theprevious steps for displaying the projected track when the user movesthe tracked object a minimum distance in the medium, and f) utilizing amotion sensor in the ultrasound probe or motion detection from the imagedata to suppress calculation and display of the track projection whenthe ultrasound probe is rotating or translating in space.

It should be understood that the present invention will be described interms of medical instruments; however, the teachings of the presentinvention are much broader and are applicable to any acousticinstruments. In some embodiments, the present principles are employed intracking or analyzing complex biological or mechanical systems. Inparticular, the present principles are applicable to internal and/orexternal tracking procedures of biological systems and procedures in allareas of the body such as the lungs, gastro-intestinal tract, excretoryorgans, blood vessels, etc. The functional elements depicted in theFIGS. may be implemented in various combinations of hardware andsoftware and provide functions which may be combined in a single elementor multiple functional elements.

The functions of the various elements shown in the FIGS. can be providedthrough the use of dedicated hardware as well as hardware capable ofexecuting software in association with appropriate software. Whenprovided by a processor, the functions can be provided by a singlededicated processor, by a single shared processor, or by a plurality ofindividual processors, some of which can be shared. Moreover, explicituse of the term “processor” or “controller” should not be construed torefer exclusively to hardware capable of executing software, and canimplicitly include, without limitation, digital signal processor (“DSP”)hardware, read-only memory (“ROM”) for storing software, random accessmemory (“RAM”), non-volatile storage, etc.

Moreover, all statements herein reciting principles, aspects, andembodiments of the invention, as well as specific examples thereof, areintended to encompass both structural and functional equivalentsthereof. Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture (i.e., any elements developed that perform the same function,regardless of structure). Thus, for example, it will be appreciated bythose skilled in the art that the block diagrams presented hereinrepresent conceptual views of illustrative system components and/orcircuitry embodying the principles of the invention. Similarly, it willbe appreciated that any flow charts, flow diagrams and the likerepresent various processes which may be substantially represented incomputer readable storage media and so executed by a computer orprocessor, whether or not such computer or processor is explicitlyshown.

Furthermore, embodiments of the present invention can take the form of acomputer program product accessible from a computer-usable orcomputer-readable storage medium providing program code for use by or inconnection with a computer or any instruction execution system. For thepurposes of this description, a computer-usable or computer readablestorage medium can be any apparatus that may include, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The medium can be an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system (or apparatus or device) or apropagation medium. Examples of a computer-readable medium include asemiconductor or solid state memory, magnetic tape, a removable computerdiskette, a random access memory (RAM), a read-only memory (ROM), arigid magnetic disk and an optical disk. Current examples of opticaldisks include compact disk-read only memory (CD-ROM), compactdisk-read/write (CD-R/W), Blu-Ray™ and DVD.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

It will also be understood that when an element such as a layer, regionor material is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, an ultrasonic diagnosticimaging system is illustratively shown in accordance with oneembodiment.

Referring first to FIG. 1, an ultrasonic diagnostic imaging systemshowing one embodiment of the present invention is shown in blockdiagram form. An ultrasound probe 10 transmits and receives ultrasoundwaves from the piezoelectric elements of an array of transducer elements12. For imaging a planar region of the body a one-dimensional (1-D)array of elements may be used, and for imaging a volumetric region ofthe body a two-dimensional (2-D) array of elements may be used to steerand focus ultrasound beams over the image region. A transmit beamformeractuates elements of the array to transmit ultrasound waves into thesubject. The signals produced in response to the reception of ultrasoundwaves are coupled to a receive beamformer 14. The beamformer 14 delaysand combines the signals from the individual transducer elements to formcoherent beamformed echo signals. When the probe includes a 2-D arrayfor 3D imaging, it may also include a microbeamformer which does partialbeamforming in the probe by combining signals from a related group(“patch”) of transducer elements as described in U.S. Pat. No.6,709,394. In that case the microbeamformed signals are coupled to themain beamformer 14 in the system which completes the beamformingprocess.

The beamformed echo signals are coupled to a signal processor 16 whichprocesses the signals in accordance with the information desired. Thesignals may be filtered, for instance, and/or harmonic signals may beseparated out for processing. The processed signals are coupled to adetector 18 which detects the information of interest. For B modeimaging amplitude detection is usually employed, whereas for spectraland color Doppler imaging the Doppler shift or frequency can bedetected. The detected signals are coupled to a scan converter 20 wherethe signals are coordinated to the desired display format, generally ina Cartesian coordinate system. Common display formats used are sector,rectilinear, and parallelogram display formats. The scan convertedsignals are coupled to an image processor for further desiredenhancement such as persistence processing. The scan converter may bebypassed for some image processing. For example the scan converter maybe bypassed when 3D image data is volume rendered by the image processorby direct operation on a 3D data set. The resulting two dimensional orthree dimensional image is stored temporarily in an image memory 24,from which it is coupled to a display processor 26. The displayprocessor 26 produces the necessary drive signals to display the imageon a docking station image display 28 or the flat panel display 38 ofthe portable system. The display processor also overlays the ultrasoundimage with graphical information from a graphics processor 30 such assystem configuration and operating information, patient identificationdata, and the time and date of the acquisition of the image.

A central controller 40 responds to user input from the user interfaceand coordinates the operation of the various parts of the ultrasoundsystem, as indicted by the arrows drawn from the central controller tothe beamformer 14, the signal processor 16, the detector 18, and thescan converter 20, and the arrow 42 indicating connections to the otherparts of the system. The user control panel 44 is shown coupled to thecentral controller 40 by which the operator enters commands and settingsfor response by the central controller 40. The central controller 40 isalso coupled to an a.c. power supply 32 to cause the a.c. supply topower a battery charger 34 which charges the battery 36 of the portableultrasound system when the portable system is docked in the dockingstation.

It is thus seen that, in this embodiment, the partitioning of thecomponents of FIG. 1 is as follows. The central controller 40,beamformer 14, signal processor 16, detector 18, scan converter 20,image processor 22, image memory 24, display processor 26, graphicsprocessor 30, flat panel display 38, and battery 36 reside in theportable ultrasound system. The control panel 44, display 28, a.c.supply 32 and charger 34 reside on the docking station. In otherembodiments the partitioning of these subsystems may be done in otherways as design objectives dictate.

Referring to FIG. 2, a diagram showing a needle tip tracking (NTT)system in communication with an ultrasound system is presented inaccordance with one embodiment.

The tracking system 200 includes an ultrasound system 210 incommunication with a needle tip tracking (NTT) module 220. The NTTmodule 220 is connected to an object, such as an NTT needle 230 via NTTcable 225. The ultrasound system 210 may include an image processor 202,a user interface 204, a display 206, and a memory 208. Additionally, anultrasound probe 205 may be connected to the ultrasound system 210. Theultrasound probe 205 may be positioned adjacent the subject 240. Thesubject 240 can be, e.g., a patient. The ultrasound probe may include amotion sensor 207. The motion sensor 207 of the probe 205 detects motionof the probe 205 with respect to the tissue of the subject 240.

The NTT needle 230 is inserted into a volume or region of interest 242of the subject 240. The needle 230 is tracked ideally from the point ofentry at the skin surface all the way to the point where it stopsinsertion. For regional anesthesia, for instance, the stopping point isnear a visualized nerve bundle, at which point the anesthetic isinjected through the needle cannula so that it optimally bathes thenerve bundle.

The distal end of the NTT needle 230 may include an ultrasound sensor234, whereas the proximal end of the NTT needle 230 may include a hub232. The distal end of the NTT needle may be, e.g., a pointed end orbeveled tip 231. Of course, one skilled in the art may contemplate anumber of different design configurations for the distal end of the NTTneedle 230. U.S. Pat. No. 9,282,946, commonly owned, and incorporatedherein in its entirety, provides further information regarding thetracking system 200 and various beamforming techniques.

Referring to FIG. 3, a diagram showing an ultrasound image depicting apair of reference lines passing as parallel tangents on opposite sidesof a location circle displayed by the system in response to the positionof the object/needle is presented in accordance with one embodiment.

The diagram illustrates an ultrasound image 305. The ultrasound image305 is shown on a screen 300 of a display device 301. The ultrasoundimage 305 depicts the NTT needle 230 travelling along a tracked path 330defined by a pair of parallel lines 310. The pair of parallel lines 310engage opposed endpoints of a location circle 320. The distal end of theNTT needle 230 includes a pointed end or beveled tip 231. The distal endof the NTT needle 230 further includes an ultrasound sensor 234. Sensor234 may comprise, in one embodiment, a single piezo electric transducerelement. A fine cable connection from sensor 234 is integrated into theNTT needle 230 and connects to NTT module 220. The ultrasound probe 205includes the motion sensor 207, which can include an accelerometer 235and a gyroscope 237 to continuously monitor movement of the ultrasoundprobe 205.

FIGS. 2 and 3 will be discussed in tandem. In the needle tracking systemthat accompanies the ultrasound scanning system, the path trackingfeature automatically displays a pair of reference lines 310 passing asparallel tangents on opposite sides of the location circle 320 displayedat the needle tip 231. The lines 310 project in the direction of thelast motion of the location circle 320 and also in the reversedirection. When the needle tip 231 is motionless for a predeterminedperiod, path tracking disappears (i.e., is not displayed on the displayscreen 300).

As the physician inserts or withdraws the needle 230, the pair of lines310 appear or are displayed, thus forming a constructed, virtual lane330 in which the needle 230 is moving, that is, a linear region, astraight path, in which the needle shaft and tip 231 proceed to move ifinsertion or withdrawal continues. The path 330 is shown when the needletip location locus meets certain conditions, such as minimum strengthand stability of the tracking signal, movement over a minimum distancein a minimally co-linear series of sample positions, etc. The path lines310 extend to the boundaries of the image 305, and may be solid, dotted,colored, etc. to indicate status, such as confidence based on trackingsignal strength.

Further, the motion sensor 207, which includes both accelerometer andgyroscope components 235, 237, is used to continuously monitor movementof the probe 205, and to suppress display of the path lines 310 if theprobe 205 is in motion, since such movement results in changes to thetracked needle position on the displayed image, independent of anyactual insertion or withdrawal of the needle. In general, detectingprobe motion causes immediate suppression of the lane lines 310, whereasmere lack of needle insertion/withdrawal results in lane displaysuppression after a number of seconds. Thus, the physician mayeffectively invoke the display of the tracked path of theinstrument/needle 230 by holding the ultrasound probe 205 steady andmoving the needle 230, per the typical workflow, yet may also pause forsome seconds to study the projected path lane 330 while not moving theneedle 230. Translation of the probe 205 in any axis is detected as achange in total force, equivalent to a change in acceleration, such thatthe magnitude of the 3-dimensional force vector deviates from 1.0 g, thebaseline gravity vector. Rotation in any axis is detected as non-zeroangular velocity, but rotation in the X axis ignored, since thatcorresponds to elevation tilt of the ultrasound probe 205, which byitself does not necessarily diminish the needle tip display norinvalidate the displayed path 330. Instead, the above mentionedconstraint on needle tracking signal strength serves to suppress thepath display as soon as pure X rotation effectively moves the needle tip231 out of the rendered image plane.

Therefore, FIGS. 2 and 3 provide a novel way of both locating andtracking the tip 231 of needle 230. The ultrasound system 210, inconjunction with probe 205, actuate a series of acoustic transmissionsthat generate 2D sweeps of scan lines or scan beams. The acoustic echodata gathered from the sweeps is detected, scan converted, and renderedas image frames on a system display as described above. Additionally, ineach sweep, the acoustic transmit beams insonicate the sensor 234 on tip231 of needle 230. The scan line with the transmit beam that is closestto the sensor 234 produces the return signal from that sensor with thehighest amplitude of the sweep. Further, the depth of the sensor 234,and therefore the tip 231, is determined from the acoustic time offlight of the transmit pulse from the probe 205 transmission surface tothe sensor 234, as indicated by the time of the return electrical signalwith respect to the time of the start of transmission at the probe inany given scan line. In this way, the system detects the location of theneedle tip as a point in the 2D sweep of scan lines, with both sweepline position coordinate and line depth coordinate. Utilizing standardscan conversion geometry, those two coordinates are transformed into thestandard Cartesian X, Y coordinates used in rendering a point. In thisembodiment, the coordinates are used as a center of a rendered circleindicating the position of the needle tip. The circle has a small radiusto represent the uncertainty arising from variations in acoustic time offlight through the tissue, from resolution limits of the scan timing,etc. The needle tip is thus represented as lying somewhere within therendered circle on the displayed image on which the circle is overlaid,frame by frame. Over a continuous series of scan sweeps, which create aseries of displayed image frames, the series of object points are thusdetected, rendered as circles on the image frames, recorded, andanalyzed for sufficiently accurate needle location detection. If theneedle does not move, the path lines or lane is suppressed (i.e., notillustrated/depicted), whereas if the needle moves, a path track isdisplayed.

To calculate the path track, a common linear regression may be utilizedon a series of the stored object points as X, Y coordinates. For aseries of N object points, the standard linear regression formula isshown below, yielding the equation for the line of the path track in thesame coordinate system. Rendering the path track on the ultrasound image305 is preferably represented by lines 310 surrounding virtual lane 330,where the line equation as calculated in the regression is furtheroffset in a direction orthogonal to its slope by a distance equal to theradius of the rendered object circle, in both positive and negativedirections.

linear regression form y=m·x+b for N value pairs of X _(i) ,Y _(i)

slope m=(NΣ _(i)(X _(i) Y _(i))−Σ_(i)(X _(i))Σ_(i)(Y _(i))/(NΣ _(i)(X_(i) ²)−Σ_(i)(X _(i))²)

intercept b=(Σ_(i)(Y _(i))−mΣ _(i)(X _(i)))/N

Besides the aforementioned motion sensor 207 in probe 205, analternative method of detecting probe motion is to detect relativemovement between image data and the ultrasound probe on a frame by framebasis. The technique performs simple image correlation to detect grossprobe motion when the ultrasound probe is coupled to the body, and canthereby suppress the display of the tracked path until the ultrasoundprobe is once again steady and the needle track has been re-established.Standard methods of correlation of image data between successive frames,optimally taken from a region of the image near the probe face, can beused to generate an average correlation of the whole frame, which isthen compared to a threshold that represents substantial image motion.If above the threshold, image motion is asserted, and display of thetracked path is suppressed.

FIG. 4 is a diagram 400 showing a needle inserted into a patient withthe ultrasound probe scanning it “in-plane” or “transverse,” inaccordance with one embodiment.

In practice, a needle 230 may be inserted into a patient 240 with theultrasound probe 205 scanning it “in-plane” or“transverse/out-of-plane.” The left-hand side illustration shows“in-plane” scanning, whereas the right-hand side illustration shows“out-of-plane” or “transverse” scanning. When scanning in-plane, themajority of the needle shaft is typically visualized (though frequentlypoorly, as mentioned previously), and insertion of the needle produces anatural projection of the path 330 of the needle shaft in the planewhere the tip may continue to appear but is in any case tracked. In thetransverse scanning position, the path 330 is mostly axial with respectto the probe face, and, thus, has a different interpretation. Whilestill representing the path of the needle tip 231, it is effectivelyshowing the projection of the path 330 on the image plane as the tip 231of the needle 230 moves from behind the plane to the front of the plane,or in the reverse direction. In this case, moderate rotation of theprobe 205 in the X axis results in generation of sufficient needle tiplocus points to display the projected vertical path. Rotation to thepoint where the needle tip signal is lost results in suppression of thepath lines 310, as is appropriate. Therefore, in summary, there is nochange to the path tracking algorithm for these two cases. Indeed, thesystem is unaware of which type of scan is chosen by the physician andthe algorithm behaves in the same manner for each scan.

Finally, the path tracking algorithm affords the needle tracking systeman improvement in tracking reliability in that spurious needle tiplocations, which are sometimes generated in the presence of simultaneousultrasound pulse reverberation and acoustic shadowing, may bebeneficially rejected if the falsely detected locations are outside ofthe previously detected path. Since the spurious detections are almostalways transient, the detected path can be used as boundaries for needletip location as long as the path is valid. Therefore, the path trackingfeature serves to enhance the reliability of the needle tracking system,as well as add utility for procedure visualization.

Referring to FIG. 5, a flow diagram showing a method for determining anddisplaying a projected track of an object/needle within a volume orregion of interest of an object is illustrated.

In block 502, measure movement from frame to frame of a detected objectpoint in a field of view by periodic comparison of positions.

In block 504, extrapolate a locus of periodically detected objectpoints.

In block 506, qualify the locus by calculating and applying a thresholdto the linearity in a sequence of positions and a threshold toconsistency in strength.

In block 508, render a plurality of lines as a path track indicator onan ultrasound image.

In block 510, display the projected track of the object when a usermoves the tracked object a minimum distance in a region of interest of asubject.

In block 512, utilize a motion sensor in an ultrasound probe or motiondetection from image data to suppress calculation and display theprojected track when the ultrasound probe is rotating or translating inspace.

In summary, in an ultrasound system which includes an object locationapparatus, wherein the object location apparatus utilizes the ultrasoundacoustic pulses generated by the ultrasound system to energize thetracking sensor, a method of automatically determining and displayingthe projected track of the object in the scanned medium is introduced.The method is self-referential in that it does not rely on an externalpositioning system to determine the validity of the detected path.Specifically, the exemplary tracking system of certain embodiments ofthe present invention requires no fixed positional reference point forthe object/needle. Instead, using the needle tracking system to get theneedle tip position in the imaging field, the tracking system operatesself-referentially in that it relies on the locus of sequentialpositions detected within the imaging field in order to display aplausible path, or suppress such a display if the locus is excessivelynon-linear or if the probe moves. The probe's motion sensor may beutilized for detection of probe movement only. In a preferredembodiment, the novel aspects include at least a) extrapolation ofun-referenced needle tip locations and/or b) qualification for thepurpose of suppression of path display via conditions such asco-linearity, signal strength, and probe movement, the latter beingdetected at least by the probe's motion sensor or by image datacorrelation. Therefore, the solution provided by the tracking system ofthe present invention is differential location from one detected pointto the next, with extrapolation and display qualification usingmeasurements of the detection signals, using path linearity, and usingprobe movement.

In some alternative implementations, the functions noted in the blocksmay occur out of the order noted in the figures. For example, two blocksshown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved.

In interpreting the appended claims, it should be understood that:

-   -   a) the word “comprising” does not exclude the presence of other        elements or acts than those listed in a given claim;    -   b) the word “a” or “an” preceding an element does not exclude        the presence of a plurality of such elements;    -   c) any reference signs in the claims do not limit their scope;    -   d) several “means” may be represented by the same item or        hardware or software implemented structure or function; and    -   e) no specific sequence of acts is intended to be required        unless specifically indicated.

Having described preferred embodiments for calculation and display of aprojected path track of object points in an ultrasound image (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments of the disclosuredisclosed which are within the scope of the embodiments disclosed hereinas outlined by the appended claims. Having thus described the detailsand particularity required by the patent laws, what is claimed anddesired protected by Letters Patent is set forth in the appended claims.

1. An ultrasound system comprising: an ultrasound probe configured toproduce acoustic transmissions and receive acoustic echo data inresponse to the acoustic transmissions; a processor coupled to theultrasound probe, the processor configured to: produce a plurality ofultrasound images based on the acoustic echo data, produce a projectedtrack of an object by: measuring movement from frame to frame of anobject point detected in a field of view by periodic comparison ofpositions of the object, extrapolating a locus of periodically detectedobject points, and providing, on the plurality of ultrasound images, apath track indicator, and suppress calculation and display of theprojected track of the object when the ultrasound probe rotates ortranslates in space; and a display coupled to the processor, the displayconfigured to display the plurality of ultrasound images, including theprojected track of the object, when a user moves the object a minimumdistance in a region of interest.
 2. The system of claim 1, furthercomprising a motion sensor in the ultrasound probe, the motion sensorconfigured to detect a motion of the ultrasound probe that is used bythe processor to suppress the calculation and display of the projectedtrack of the object.
 3. The system of claim 2, wherein the motion sensorincludes an accelerometer and a gyroscope configured to continuouslymonitor movement of the ultrasound probe.
 4. The system of claim 1,wherein the processor is configured to detect a motion of the ultrasoundprobe from image data and use the detected motion to suppress thecalculation and the display of the projected track of the object.
 5. Thesystem of claim 4, wherein the processor is configured to detect amotion of the ultrasound probe based on detection of relative movementbetween the image data and the ultrasound probe on a frame by framebasis.
 6. The system of claim 1, wherein the path track indicatorcomprises a rendering of a plurality of lines and the plurality of linescomprises a pair of reference lines separate from the object andpositioned on opposite sides of the object to indicate the projectedtrack of the object.
 7. The system of claim 6, wherein the processor isfurther configured to render a location circle to locate the object inthe plurality of ultrasound images and render the pair of referencelines as parallel tangents on opposite sides of the location circle. 8.The system of claim 6, wherein the processor is configured to render thepair of reference lines projected in a direction of a last motion of thelocation circle.
 9. The system of claim 6, wherein the processor isconfigured to render the pair of reference lines to form a virtual lanethat extends up to a boundary of one or more images of the plurality ofultrasound images.
 10. The system of claim 6, wherein, when the objectis motionless, the processor is configured to display the pair ofreference lines for a predetermined period of time for observation bythe user.
 11. The system of claim 1, wherein the processor is furtherconfigured to qualify the locus by calculating and applying a thresholdto a linearity in a sequence of positions and a threshold to consistencyin strength of the detected object point.
 12. A controller for trackingan object, the controller comprising: at least one processor configuredto: produce a plurality of ultrasound images based on acoustic echo datareceived by an ultrasound probe, produce a projected track of an objectby: measuring movement from frame to frame of an object point detectedin a field of view by periodic comparison of positions of the object,extrapolating a locus of periodically detected object points, andproviding, on the plurality of ultrasound images, a path trackindicator, display the projected track of the object when a user movesthe object a minimum distance in a region of interest; and suppresscalculation and display of the projected track of the object when theultrasound probe rotates or translates in space.
 13. The controller ofclaim 12, wherein the path track indicator comprises a rendering of aplurality of lines and the plurality of lines comprises a pair ofreference lines separate from the object and positioned on oppositesides of the object to indicate the projected track of the object. 14.The controller of claim 13, wherein the processor is further configuredto render a location circle to locate the object in the plurality ofultrasound images and render the pair of reference lines as paralleltangents on opposite sides of the location circle.
 15. The controller ofclaim 13, wherein the processor is configured to render the pair ofreference lines projected in a direction of a last motion of thelocation circle.
 16. The controller of claim 13, wherein the processoris configured to render the pair of reference lines to form a virtuallane that extends up to a boundary of one or more images of theplurality of ultrasound images.
 17. The controller of claim 13, when theobject is motionless, the processor is configured to display the pair ofreference lines for a predetermined period of time for observation bythe user.
 18. The controller of claim 12, wherein the processor isfurther configured to qualify the locus by calculating and applying athreshold to a linearity in a sequence of positions and a threshold toconsistency in strength of the detected object point.
 19. The controllerof claim 12, wherein the processor is further configured to utilize amotion signal obtained from a motion sensor in the ultrasound probe ormotion detected from image data to suppress the calculation and thedisplay of the projected track of the object.
 20. A method for trackingan object, the method comprising: producing a plurality of ultrasoundimages based on the acoustic echo data received by an ultrasound probe,producing a projected track of an object by: measuring movement fromframe to frame of an object point detected in a field of view byperiodic comparison of positions of the object, extrapolating a locus ofperiodically detected object points, and providing, on the plurality ofultrasound images, a path track indicator, displaying, on a display, theprojected track of the object when a user moves the object a minimumdistance in a region of interest; and suppressing calculation anddisplay of the projected track of the object when the ultrasound proberotates or translates in space.